Spinning of high nitrogen content cellulose nitrate filments



3 256,371 SPINNING or HIGH NITROGEN CONTENT CELLULOSE NITRATE FILAMENTS Richard N. Rulison, Gillette, N.J., assignor to Celanese Corporation of America, New York, NY, a corporation of Delaware No Drawing. Filed Jan. 18, 1963, Ser. No. 252,513

19 Claims. (Cl. 264-3) This application is a continuation-in-part of application Serial No. 629,237, filed December 19, 1956, now abandoned.

This invention relates to the making of filamentary material from cellulose nitrate.

It is an object of this invention to provide a novel method for the production of strong continuous filaments of cellulose nitrate of high nitrogen content.

Other objects of this invention will be apparent from the following detailed description and claims. In this description and claims all proportions are by weight unless otherwise indicated.

In accordance with one aspect of this invention, a solution of a cellulose nitrate of at least 12.5% nitrogen content in an organic solvent is extruded under pressure through a small orifice and into and through a bath of liquid coagulant for said solution. In many cases, particularly when lower denier material, e.g., up to 20 to 50 denier per filament (d.p.f.), is being spun, the yarn may be stretched during its passage through said bath of coagulant. Preferably, the extrusion takes place simultaneously through a number of adjacent orifices to produce a plurality of continuous filaments which, after emerging from the bath of coagulant, are taken up as a yarn.

The liquid coagulant is an organic liquid having some swelling power for the cellulose nitrate of at least 12.5% nitrogen content. When a relatively low denier material is being spun, e.g., up to 20 or 50 denier per filament, best results are usually obtained by the use of liquid coagulants comprising major proportions of methanol or ethanol. The yarn emerges from the bath of liquid coagulant ina condition in which its individual filaments tend to adhere to each other on drying. Such adhesion is avoided by washing the yarn with water, or other strongly acting non-solvent miscible with said coagulant, before drying and preferably before the yarn is wound in a package or otherwise collected.

By the process of this invention, there are obtained yarns having tenacities of at least 1.5 grams per denier and elongations at break of above 10%. Under optimum conditions, a tenacity in excess of 2.5 grams per denier, e.g., a tenacity of 2.9 grams per denier at an elongation of 18% has been attained. These yarns are of sufiicient strength to permit them to be wound into very tight packages and to be woven or knitted to form strong textile fabrics, without any saponification to convert the cellulose nitrate to cellulose. These fibrous products are highly combustible and are useful, for example, as explosives and propellants.

The solution being extruded, hereinafter termed the spinning dope, is generally a relatively viscous solution, e.g., a solution containing about 15 to 30% of the cellulose nitrate of at least 12.5 nitrogen content and having a viscosity of about 300 to 10,000 poises.

In one advantageous embodiment of the invention, the solvent in the spinning dope is primarily acetone, e.g., at least 50%, though minor amounts of ethanol and United States Patent small amounts of water may be present, although the dope solvent may contain as much as 12% of water in some instances, it usually contains a considerably smaller amount, e.g., up to 5% and preferably 0.5 to 3.0% of water, based on the weight of the solvent. This allows for less sensitivity of spinning stability and yarn quality to composition of the coagulation bath and for better overall yarn quality. The liquid coagulant for this dope comprising an acetone-based solvent may contain about 65 to of methanol, about 5 to 12% of water and the balance acetone when a relatively low denier material, e.g., of up to 20 or 50 d.p.f., is being spun. A mixture of methanol and about 1 to 9% of water, without acetone, also has given good results in the case of a nitrocellulose of 12.65% nitrogen content, while methanol containing as little as a few tenths of one percent of water (e.g., 0.4% water) has given good results with cellulose nitrates of higher nitrogen contents. Ethanol has also proved tobe very suitable as the coagulant, particularly for spinning-dopes containing cellulose nitrates of extremely high nitrogen content, e.g., cellulose nitrate of 13.1% nitrogen content. The ethanol is preferably mixed with a small amount of acetone, e.g., 2l0'%. Even higher proportions of acetone, e.g., up to about 25%, may be used in combination with the ethanol when water is present; here the proportion of Water is small, e.g., up to about 10%. v The temperature of the liquid coagulant and of the spinning dope may be varied as desired; one suitable range is about 10 C. to 60 C.

The degree of stretching of the filaments in the bath of liquid coagulant is measured by the draw-down ratio, which relates the linear speed at which the filaments are taken up after passing through said bath to the linear speed at which the spinning dope is forced through the spinning orifices. Draw-down ratios ranging from about 2.5 :1 to over 100:1 have given good results.

The following examples are given to illustrate this invention further.

' Example I Cellulose nitrate having a nitrogen content of 12.65

Model RVF, Spindle No. 7, at 4 r.p.m. and at 25 C.), is

extruded through a spinning jet having 40 holes, each of 0.15 mm. diameter, into a bath of liquid coagulant having a temperature of 22 C. The coagulant contains 836% by weight of methanol, 7.4% of water and 9.0% of acetone. The resulting filaments pass substantially horizontally through centimeters of the bath of coagulant and after emerging therefrom are taken up as a 40- fila'ment yarn on a driven rotating roll wet with water. When the rate of take up is meters per minute, and the draw-down ratio is 6.311, the denier per filament of the yarn is 4.0 and the resulting yarn has a tenacity of 2.66'grams per denier and an elongation at break of 13.2%. When the rate of take up is 76 meters per minute and the draw-down ratio is 4.3:1 the denier per filament is 5.9, the tenacity is 2.55 grams per denier and the elongation is 15.9%. At a take-up speed of 127 meters per minute and a draw-down ratio of 7.121, the denier per filament is 3.6, the tenacity 2.61 grams per denier and the elongation 12.4%. All tenacity and elongation measurements are made on yarn unwrapped from the take-up roll and air-dried in a relaxed condition.

33 Example II Cellulose nitrate having a nitrogen content of 13.13% and a degree of polymerization of 318, dissolved in a solvent mixture of 92.2% acetone, 6.7% ethanol and 1.1% water to form a spinning dope having a viscosity of 1530 poises (measured as in Example I), is extruded through a spinning jet having a single hole 0.1 mm. in diameter into a bath of coagulant having a temperature of 21 C. The coagulant contains 99.6% methanol and 0.4% water. The resulting filament passes substantially horizontally through 87 centimeters of this bath and, after emerging therefrom, is taken up on a driven rotating roll wet with water. The take-up speed and draw-down ratio are varied, with the results indicated below, all

measurements being made as in Example I:

Take-up speed Draw- Filament, Tenacity Elongation (Meters per minute) down Denier (Grams per (Percent) ratio Denier) Example III Example II is repeated, except that the spinning jet has a single hole 0.3 mm. in diameter, the bath of coagulant is at 22 C., the take-up speed is 40 meters per minute and the draw-down ratio is 118:1. An 0.85 denier filament having a tenacity of 2.32 grams per denier and an elongation of is obtained.

Example IV Example I is repeated except that the spinning jet has 20 holes each 0. 2mm. in diameter and the bath of coagulant contains 83.7% methanol, 8.6% water and 5.7% acetone, at a temperature of 21 C.; the filaments travel 100 cm. through the bath. At a take-up speed of 75 meters per minute and a draw-down ratio of 10.3:1 there is obtained a 20-fi1ament yarn of 88 total denier having a tenacity of 2.60 grams per denier and an elongation of 16.7%.

Example V Example II is repeated except that the hole is 0.2 mm. in diameter; the bath of coagulant, which is at a temperature of 23 C., contains 70.8% ethanol, 23.2% acetone and 6% water; and the filament travels 90 centimeters in said bath. At a take-up speed of 50 meters per minute and a draw-down ratio of 15.2, a 2.95 denier filament having a tenacity of 1.94 grams per denier and an elongation of 17.1% is obtained.

Example VI Example VII The cellulose nitrate described in Example I (12.65% nitrogen) was dissolved in a solvent consisting of 83.3% of acetone, 15.5% of ethanol and 1.2% of water to yield a solution having .a solids content of 24.8% and a viscosity of 1590 poises at 25 C. The solution was extruded through a spinning jet having an orifice of 0.1 mm. diameter in a horizontal direction into a coagulation bath consisting of 9.8% of water, 12.4% of acetone and 77.8% of methanol at a temperature of 23 C. The resulting filament was taken through the coagulation bath for a distance of cm. and was taken up at a speed of 75 meters/minute at a draw-down ratio of 46:1. The

denier of the filament was 3.82, the tenacity was 2.9 grams 1 .per denier and the elongation was 18.0%

ing a relatively high percentage of water resulted in generally higher sensitivity of spinning stability and lower yarn quality due to excessive interfilament cohesion than when the spinning solution contained a smaller amount of water.

In accordance with another aspect of the invention, filarnents of cellulose nitrate containing at least 12.5% of nitrogen may be spun from a spinning dope containing a major amount of lower alkanol, e.g., methanol, and minor amounts of acetone and water. Although the use of a solvent containing a major amount of acetone results in a product having maximum tenacity, there are applications for which such maximum tenacity may not be necessary. In that case, the use of a substantial .or major amount of a lower alkanol, e.g., methanol or ethanol in the spinning solvent results in a considerable economic advantage due to a reduced rate of accumulation of acetone in the coagulation bath. For example,

the solvent may contain 40 to 100%, preferably 64 to 94.5% of methanol, up to 50%, preferably 5 to 30% of acetone, and up to 10% preferably 0.5 to 3% of water. The coagulation bath when this type of spinning dope is used may have a composition comprising the same components within the same percentage ranges as described above in connection with the spinning of a dope containing a major amount of acetone in the solvent.

The following example illustrates the spinning of a product from a spinning solution comprising a solvent made up of a major amount of a lower alkanol, i.e., methanol.

Example VIII The cellulose nitrate described in Example I, was dissolved in a solvent consisting of 76.5% of methanol, 21% of acetone and 2.45% of water to yield a solution having a solids content of 23.5% and a viscosity at 25 C. of 1,870 poises. This solution was extruded through a jet hole of 0.1 mm. diameter into a coagulation bath consisting of 78.3% of methanol, 12.4% acetone and 9.3% water at a temperature of 27 C. The resulting filament traveled through the coagulation bath in a horizontal direction for a distance of 100 cm. and was taken up at a spinning speed of 75 meters per minute at a draw-down ratio of 4.8:1 to yield a filament having a denier of about 3.5, a tenacity of about 2.0 grams per denier and an elongation of about 21%.

In accordance with still another aspect of the invention, the cellulose nitrate of high nitrogen content is dissolved in a solvent comprising a major amount of a lower alkanol ester of a lower alkanoic acid, e.g., ethyl acetate or methyl acetate to form a spinning solution. The spinning solvent may be composed solely of said ester or may contain, for example, up to 12% of a lower alkanol, e.g., ethanol or methanol and/or up to 3% of water. The coagulation bathmay be composed of the same components within the same percentage ranges as that described previously in connection with dopes containing a major amount of acetone in the spinning solvent. Alternatively, the acetone in the bath may be replaced by the ester being employed as the solvent, which ester may then be used in an amount within the same range as that set out above for acetone in the coagulation bath.

The following examples illustrate the formation of cellulose nitrate fibers from solution in a solvent comprising a major amount of a lower alkanol ester of a lower alkanoic acid.

Example IX The cellulose nitrate described in Example I, was dissolved in a solvent of methyl acetate to yield a spinning solution containing 23.0% of solids and having a viscosity at 25 C. of 6,840 poises. The solution was extruded in a horizontal direction through a jet of 0.1 mm. diameter into a coagulation bath consisting of about 77.1% of methanol, about 14.2% of methyl acetate, and about 8.7% of water at 25 C. The resulting filament traveled in a horizontal direction through the coagulation bath for a distance of 100 cm. and was taken up at a speed of 75 meters/minute at a draw down ratio of 3.9: 1. The filament had a denier of about 4.7, a tenacity of 2.8 grams per denier and an elongation of 16.6%.

Example X The procedure of Example IX was repeated, except that the spinning solvent was ethyl acetate, the solids content of the dope was-20.5% and the coagulation bath consisted of over 90% of methanol, 7% of water, and a small amount of ethyl acetate and the draw-down ratio was 8.5 :1. The filament was obtained having a denier of 1.9, a tenacity of 2.5 grams per denier and an elongation of 13.0%.

In accordance with another aspect of the invention, filaments of cellulose nitrate of high nitrogen content, e.g., at least 12.5% nitrogen may be formed into filaments of relatively high denier, e.-g., 60 to 2,000 denier, by dis solving the cellulose nitrate in a suitable solvent, e.g., any of those described above such as those containing a major amount of acetone or methanol, to yield a spinning solution having a relatively high viscosity, e.g., 4,000 to 10,000 poises at 25 C. The solution is then extruded through holes having a diameter of 0.1 to 1 mm. into a coagulation bath comprising a major amount of water. The bath may also contain minor amounts of other compounds, e.g., up to 10% of acetone and/or up to 15% of lower alkanol, and taken up at a speed of 10 to 30 meters/ minute, with the lower part of the range of spinning speed being preferably used for the upper part of the stated range of deniers and vice versa, and the filamentary material being allowed to remain immersed in the coagulation bath for a period of at least 3 seconds, preferably 5 to 60 seconds. The high denier material is generally not completely coagulated when it leaves the coagulation bat-h. To completely coagulate the material, it is generally washed with water, e.g., While it is wrapped around skewed rolls. The material generally is contacted with wash water after it leaves the coagulation bath for a period of at least 2 minutes, preferably 5 to 30 minutes. The resulting filaments often have an approximately rectangular cross-section.

The higher denier material described above is useful in applications requiring a substantially lower surface to volume ratio than lower denier material. For example, it is useful in applications requiring a substantially lower combustion rate than the lower denier material.

The following example illustrates the spinning of relatively high denier material:

Example XI The cellulose nitrate described in Example I was dissolved in a solvent consisting of 90.5% of acetone, 8% of ethanol and 1.5% of water to'yield a solution containing 27% of solids and having a viscosity of 6,300 poises at 25 C. The solution was extruded in a vertically upward direction through a spinnerette containing 5 holes, each 0.5 mm. in diameter into a coagulation bath of water 6 containing 2.5% of acetone at 25 C. The length of the coagulation bath was 150cm. and the material was taken up at a speed of 11 meters/minute at a draw-down ratio of 3:1. The material was washed for 20 minutes with water on skewed rolls. It had a denier of 1000, and an approximately rectangular cross-section of 150 by 500 microns dimension.

It is often desirable for filaments of cellulose nitrate of high nitrogen content to contain various additive materials, e.g., a stabilizer, a combustion deterrent which often also acts as a cooling agent, and in some cases another highly combustible or explosive material which acts as a combustion and/ or energy modifier. The stabilizer may be present in the filamentary material, for example, in an amount of 0.5 to 2% based on the weight of the cellulose nitrate and may be, for example, diphenylamine, ethyl centralite or methyl centralite. A combustion deterrent may be present in the filament, for example, in an amount of 2 to 10% based on the weight of the cellulose nitrate and may be, for example, dibutyl phthalate.

The additional highly combustible material present in the cellulose nit-rate filaments may be present, for example, in an amount of 5 to 15 based on the weight of the cellulose nitrate. Compounds such as dinitrotoluene or nitroglycerine may be used for this purpose.

In accordance with still another aspect of the invention, filaments of up to 50 denier are produced containing at least one additive, e.g., within the above percentage ranges, byadding the additive directly to the coagulation bath. For example, the process may be carried out by controlling the composition of the coagulation bath such that it contains 0.1 to 0.6% of a stabilizer such as diphenylamine. If desired, the composition of the bath may also be controlled such that it contains 0.5 to 3% of a combustion deterrent such as dibutyl phthalate and/ or 1 to 4% of an additional highly combustible material such as dinitrotoluene. Surprisingly, it has been found that controlling the composition of the coagulation bath in this manner results in filaments containing requisite amounts of additive materials, whereas controlling the amount of additives in the spinning dope often does not result in the required amounts of additives being present in the filamentary product. Moreover, controlling the amount of additive'in the coagulation bath results in a filament containing the additive substantially uniformly distributed throughout its cross-section as distinguished from subsequent application of additive to an already formed filament, in which case the additive is distributed substantially near the periphery of the filament, with little in the interior.

The following example illustrates the production of filamentary material containing desired amounts of additives, by controlling the composition of the coagulation bath:

Example XII The cellulose nitrate described in Example II (16.13% nitrogen), diphenylamine, dibutylphthalate, and dinitrotoluene were dissolved in a spinning solvent consisting of 91% of acetone, 8% ethanol, and 1% of water to yield a spinning solution containing 22.7% of cellulose nitrate based on the weight of the solution, 10.0% of dinitrotoluene, 5.0% of dibutyl phthalate and 1.0% of diphenylamine, the last three percentages being based on the weight of the cellulose nitrate. The total non-volatile content of the solution was 216.3% and its viscosity was 2150 poises at 25 C. The solution was extruded in a vertically upward direction through a spinnerette containing 400 holes, each microns in diameter, into a spin bath consisting of 19.8% acetone, 5.7% of water, 2.7% of dinitrotoluene, 1.5 dibutyl phthalate and 0.279% of diphenylamine and the balance methanol, at 25 C. The column containing the coagulation bathwas cm. long and the yarn was taken up at spinning speed of 77 meters/minute at .a draw-do wn ratio of 2.9: l. The

7 yarn had a total denier of 1,425 (6.56 d.p.f.), and contained 10.0% of dinitrotoluene, 5.7% of dibutyl phthalate -and 0.91% of diphenylamine distributed substantially uniformly throughout the cross-section of the filaments.

The filaments produced by the process of this invention wherein the coagulation bath contains a major amount of a lower alkanol, e.g., as described in Example I, have a substantially round cross-section and-a surface appearance when examined with an optical microscope which has a higher degree of roughness than most manrnade filaments. The surface may also be described as highly pitted or eroded, i.e., having the appearance, for example, of a metal surfaceeroded by acid.

The rough surface structure of the material contributes to its effectiveness as an explosive and/or propellant where such structure allows for quick and reliable ignition.

The rough surface also assists physical bonding among the filaments and between the filament and other materials. This feature is of particular value when the filarnent is fashioned into structures incorporating another material.

It is to be understood that the foregoing detailed description is given merely by way of illustration and that many variations may be made therein without departing from the spirit of my invention.

Having described my invention what I desire to secure by Letters Patent is:

1. A process for the production of yarns of high tenacity which comprises extruding a solution of cellulose nitrate of at least 12.5% nitrogen content through a spinning orifice into and through a bath of a liquid coagulant for said solution containing a stabilizer for said cellulose nitrate, said yarns containing said stabilizer.

'2. The process of claim 1, wherein said cellulose nitrate is dissolved in a solvent comprising a major amount of a lower alkyl ester of a lower alkanoic acid.

3. The process of claim 1, wherein said cellulose nitrate is dissolved in a solvent comprising a major amount of a lower alkanol.

-4. The process of claim 1, wherein the spin bath is controlled such that it contains 0.1 to 0.6% of diphenylamine, 0.5 to 3% of dibutyl phthalate, and 1 to 4% of dinitrotoluene.

5. A process for the production of yarns of high tenacity which comprises extruding a solution of cellulose nitrate of at least 12.5 nitrogen content through a spinning orifice into and through a bath of a liquid coagulant for said solution comprising principally a lower alcohol, small amount of water, and a stabilizer for said cellulose nitrate selected from the group consisting of diphenyl amine, ethyl centralite and methyl centralite and stretching the'resulting filament in said bath said yarns containing said stabilizer.

6. A process comprising extruding a solution of cellulose nitrate of at least 12.5% nitrogen content in a solvent comprising a major amount of acetone through a spinning orifice into and through a bath of liquid coagulant for said solution comprising at least 65% of an alkanol having 1 to 2 cabon atoms and a stabilizer for said cellulose nitrate, any remaining component selected from the group consisting of acetone, water and mixtures thereof, and stretching the resulting filament in said bath said filament containing said stabilizer.

7. Process as set forth in claim 6 in which said coagulant is principally methanol and contains a small amount of water.

8. Process as set forth in claim 6 in which said coagulant is principally ethanol.

9. Process as set forth in claim 6 in which said coagulant is principally methanol and contains a small proportion of acetone.

10. Process as set forth in claim 6 in which said coagulant is principally ethanol and contains a small proportion of acetone.

11. Process as set forth in claim 6 in which said coagulant comprises at least about 91% of methanol.

12. Process for the production of strong filaments of tenacity of at least 1.5 grams per denier which comprises extruding a 15-25% solution of cellulose nitrate of 12. 65 nitrogen content in a solvent containing a major amount of acetone and a minor amount of ethanol through a spinning orifice and into and through a bath of coagulant comprising about 65 to of methanol, about 5 to 12% of water, a stabilizer for said cellulose nitrate and the balance acetone, and stretching the resulting filament in said bath said filament containing said stabilizer.

13. Process for the production of strong filaments of tenacity of at least 1.5 grams per denier which comprises extruding a 15-30% solution of cellulose nit-rate of 13.13% nitrogen content in a solvent containing acetone and a minor amount of ethanol through a spinning orifice, and into and through a bath of coagulant comprising a major proportion of methanol, a minor proportion of acetone, and a stabilizer for said cellulose nitrate and stretching the resulting filament in said bath said filaments containing said stabilizer.

14. The process for the production of filamentary material having a denier/filament of at least 60 which comprises extruding a solution of cellulose nitrate of at least 12.5% nitrogen content through an orifice into and through a bath composed principally of water and a stabilizer for said cellulose nitrate, said filamentary material containing said stabilizer.

15. The process of claim 14 wherein said orifice has a diameter of 0.1 to 1 mm, said material remains in contact with said bath for a period of at least 3 seconds, said material is taken up at a speed of 10 to 30 meters/minute and said material is washed with water for a period of at least 2 minutes.

16. A process for the production of yarns of high tenacity which comprises extruding a solution of cellulose nitrate of at least 12.5% nitrogen content through a spinning orifice into and through a bath of a liquid coagulant for said solution containing a combustion deterrent for said cellulose nitrate, said yarns containing said combustion deterrent.

17. The process of claim 16 wherein said combustion deterrent is dibutyl phthalate.

18. A process for-the production of yarns of high tenacity which comprises extruding a solution of cellulose nitrate of at least 12.5% nitrogen content through aspinning orifice into and through a bath of a liquid coagulant for said solution containing an additional highly combustible material, said yarns containing said additional highly combustible material. 1

19. The process of claim 18 wherein said additional highly combustible material is selected from the group consisting of dinitrotoluene and nitroglycerine.

References Cited by the Examiner UNITED STATES PATENTS 562,626 6/1896 Lehner 264-187 843,556 6/1916 Isler 264-487 1,562,076 11/1925 Bindschedler 1854 1,584,005 5/ 1926 Bindschedler 264187 1,679,850 8/1928 Berl 264-200 1,978,741 10/1934 Delpech et al. 18-54 2,033,217 3/1936 Woodbridge 14911 2,122,448 7/ 1938 Berl 18-54 2,153,331 4/ 1939 Kunz 14996 2,289,520 7/ 1942 Reichel et al. l8-54 2,3 8 1,468 8/ 1945 Silk 14997 2,517,694 8/1950 Merion et al. 28-82 2,715,763 -8/1955 Marley 28-82 (Other references on following page) 11/ 1905 Great Britain.

10/ 1937- Great Britain.

- 3,256,371 9 10 UNITED STATES PATENTS OTHER REFERENCES 12/1959 Stewart et a1 149-97 B-arsha, Nitrocellulose, Colloid Chemistry, vol. 6,

7/1961 Nadel 149-2 pages 860-86 (1946). 6/1964 De Fries 149-11 5 ALEXANDER H. BRODMERKEL, Primary Examiner.

MORRIS LIE/BMAN, ROBERT F. WHITE, CHARLES B. HAMBURG, KENNETH W. VERNON,

Assistant Examiners.

FOREIGN PATENTS 8/1926 Great Britain. 

1. A PROCESS FOR THE PRODUCTION OF YARNS OF HIGH TENACITY WHICH COMPRISES EXTRUDING A SOLUTION OF CELLULOSE NITRATE OF AT LEAST 12.5% NITROGEN CONTENT THROUGH A SPINNING ORIFICE INTO AND THROUGH A BATH OF A LIQUID COAGULANT FOR SAID SOLUTION CONTAINING A STABILIZER FOR SAID CELLULOSE NITRATE, SAID YARNS CONTAINING SAID STABILIZER. 